What is the importance of the citrate utilization test in Enterobacteriaceae identification?

• A. It determines their antibiotic susceptibility
• B. It differentiates between bacteria that can utilize citrate as their sole carbon source
• C. It assesses their ability to produce gas
• D. It identifies the production of urease

Answer: (B)

The citrate utilization test is significant in the identification of Enterobacteriaceae because it specifically differentiates between bacterial species based on their ability to use citrate as their only source of carbon. In environments where glucose and other carbohydrates are limited, some bacteria possess the metabolic capability to convert citrate into energy, which is crucial for their survival and growth.

When conducting the citrate utilization test, organisms that can utilize citrate grow on a medium that contains citrate and produce alkaline byproducts that lead to a color change in the medium, typically from green to blue. This color shift indicates that the bacterium has succeeded in metabolizing citrate.

This test helps distinguish species such as Citrobacter and Klebsiella, which can utilize citrate, from others that cannot. Understanding the metabolic capabilities of different Enterobacteriaceae is fundamental for proper identification and classification within clinical microbiology and can guide appropriate treatment options.

Other options do not relate to the core purpose of this particular test; hence, they do not contribute to the relevance of the citrate utilization test in the context of Enterobacteriaceae identification.